<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  #box{
    width:800px;
    height:800px;
    background: url(
    'https://img.tupianzj.com/uploads/allimg/202012/9999/950b992764.jpg');
    margin: 50px auto;
  }
  #box2{
    width:800px;
    height:800px;
    background: url('https://img.tupianzj.com/uploads/allimg/202102/9999/8b45bc942e.jpg');
    margin: 50px auto;
  }
  #box3{
    width:800px;
    height:800px;
    background: url('https://img.tupianzj.com/uploads/allimg/202103/9999/914fab1997.jpg');
    margin: 50px auto;
  }
  #box4{
    width:800px;
    height:800px;
    background: url('https://img.tupianzj.com/uploads/allimg/202004/9999/bae7f62401.jpg');
    margin: 50px auto;
  }
</style>
<body>
  <div id="app">
    <button @click="change">显示</button>
    <div id="box"  v-if="num%4 === 0"></div>
    <div id="box2" v-else-if="num%4===1"></div>
    <div id="box4" v-else-if="num%4===2"></div>
    <div id="box3" v-else></div>
  </div>
  <script src="./vue.js"></script>
  <script>

    const vm = new Vue({
      el: '#app',
      data: {
        num: 0
      },
      methods: {
        change(){
          this.num++;
        }
      }
    })
    // btn.addEventListener('事件',回调函数,[false/true])
  </script>
</body>
</html>